Fix bugs in monitor

monitor/default_test.go

@@ -12,8 +12,20 @@ func TestMonitor(t *testing.T) {
 
 	for _, service := range services {
 		_, err := m.Status(service)
-		if err != nil {
+		if err == nil {
 			t.Fatal("expected status error for unknown service")
 		}
+
+		if err := m.Watch(service); err == nil {
+			t.Fatal("expected watch error for unknown service")
+		}
+
+		// TODO:
+		// 1. start a service
+		// 2. watch service
+		// 3. get service status
 	}
+
+	// stop monitor
+	m.Stop()
 }